By raising apāna and bringing prāṇa down from the throat, the yogi, freed from old age, becomes about sixteen years old.

This verse expands the pranic mechanism of Mūla Bandha.The technique reverses the natural flows of the two main currents: apāna, which normally descends towards the organs of elimination, is raised upward, while prāṇa, which tends to disperse in the thoracic and cranial region, is directed downward.

This reversal of pranic polarities is a fundamental principle of haṭha yoga.When the two currents meet in the region of the navel—the manipūra cakra—they generate intense heat (tapas) that activates dormant kuṇḍalinī in mūlādhāra.

Ṣoḍaśābdavayaḥ — the age of sixteen represents the peak of youthful vitality according to tradition.It should not be interpreted literally as physical rejuvenation, but as the recovery of the energetic fullness characteristic of youth: flexibility, vigor, mental clarity and vital enthusiasm.